This invention relates to a sample cup for use in holding specimens for spectrochemical analysis and more particularly to such a cup including means for venting the same.
Sample cups for spectrochemical analysis are used in the prior art to hold or contain liquids, solids and powdered specimens under normal atmospheric pressure, gas pressure or in vacuum for analysis such as energy and wavelength dispersion and optical emission methods. These cups are in wide spread use and have been the subject matter of many patents.
A basic sample cup consists of three components as a cup-shaped cell body having closed bottom and an opened top, an annular collar and a snap-on ring. The collar and the snap-on ring serve to secure a sheet of plastic material such as MYLAR, a trademark for a polyester sheet material of E. I. duPont de Nemours and Company, to cover the open top of the cell when the hollow of the cell is filled with a specimen to be analyzed. Such cells are available from many sources such as Chemplex Industries, Inc., 140 Marbledale Road, Eastchester, N.Y. 10707, the assignee herein.
The cells of the priar art typically have venting means which may comprise a smaller area on the closed bottom surface of the cell which can be punctured or pierced by means of a sharp point such as a needle, a ballpoint pen or some other device. The pierced hole serves as a vent which is used to equalize pressure which is in the sample cup.
An example of a typical venting means is shown in U.S. Pat. No. 4,409,854 entitled Sample Cup with Venting Means for Use in X-ray Spectroscopy, issued on Oct. 18, 1983 to Michael C. Solazzi and assigned to the assignee herein.
During the spectrochemical analytic investigation of specimens characterized with high abrogation properties in air, the entire assembed sample cup with the plastic sheet covering the cup is emplaced within a vacuum or an inert gas environment.
Under conditions where pressure equalization is not implemented, the plastic sheet will distend or bow outwardly due to the vacuum or lower pressure. This then places the surface of the sheet closer to the excitation source which may be an x-ray tube or other device. The surface of the sheet of plastic is commonly defined as the sample plane. Thus a variation in the distance from the sample plane to the source of excitation operates to alter the intensity of the characteristic radiation of the specimen and also the intensity of radiation impinging upon the sample from the excitation source.
The variations result in erroneous quantatative data and hence cannot be tolerated. As indicated, for applications in a vacuum environment, the thin plastic film distends or bows out (convex) which decreases the distance from the sample to the excitation soruce. For applications in a gaseous environment (positive pressure) the thin plastic film distends or is drawn into the hollow of the cell providing a concave surface. This effect increases the distance between the sample plane and the excitation source resulting in lower values of analytical data.
In order to equalize the pressure, the prior art had a section in the closed bottom surface of the cell which allowed one to pierce a hole in the cup or vent the cup. This technique relied upon the skill of the operator, and if too much force were employed, the hole would be too large and a sample might become contaminated or parts of the cup dislodged.
In other prior art techniques such as the techniques referred to in the above noted patent, the venting means were relatively complicated resulting in difficulty and in increased cost in molding and providing such structures. Other techniques such as that shown in U.S. Pat. No. 4,346,299 entitled Cell for Containing Fluid to be Analyzed by X-ray Spectroscopy, issued on August 1982 to A. J. Mittledorf et al show venting means which are disposed off center and which include a vertical pin or post which is also off center on a generally circular structure which defines the puncturing means.
In this patent the puncturing means includes a semi-circular portion of minimal thickness which provides an area of weakness and another semi-circular portion of a greater thickness. Located between the two areas in an upstanding post which when pivoted in the direction of the thick wall causes the thin wall to rupture and hence provide a venting means. This technique is particularly difficult to utilize as it requires a pivoting motion of the pin, and hence the operator may drop the cup or the pivoting motion may cause an excessive material loss while providing possible sample contamination.
It is, therefore, an object of the present invention to provide a sample cup including improved venting means which enable an operator to provide venting of the cup in a rapid and precise manner.